Imaging of Endogenous Hydrogen Peroxide during the Process of Cell Mitosis and Mouse Brain Development with a Near-Infrared Ratiometric Fluorescent Probe

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

A novel AIE fluorescent probe for the detection and imaging of hydrogen peroxide in living tumor cells and in vivo

Hydrogen peroxide (H2O2), a key reactive oxygen species (ROS), plays crucial roles in redox signaling pathways and immune responses associated with cell proliferation, differentiation, migration, and disease progression. The selective monitoring of overproduced H2O2 is important for understanding the diagnosis and pathogenesis of diseases such as cardiovascular disease, cancers, diabetes, Parkinson's disease, Alzheimer's disease, and inflammation. In this paper, an AIE fluorescent probe BQM-H2O2 was developed by connecting phenyl borate with the fluorophore BQM-PNH for selective detection of H2O2. In the presence of H2O2 at fw = 99% (pH = 7.4, 1% DMSO), the probe BQM-H2O2 could generate strong fluorescent signals due to the oxidation of the borate ester. The probe exhibited high selectivity and a low detection limit toward H2O2 with the calculated LOD of 112.6 nM. Importantly, it was employed in the detection of exogenous and endogenous hydrogen peroxide in 4T1 cells with low cytotoxicity. This probe has also been successfully applied to imaging of H2O2 in Blab/c mice bearing 4T1 graft tumors.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Mitochondria-Targetable Near-Infrared Fluorescent Probe for Visualization of Hydrogen Peroxide in Lung Injury, Liver Injury, and Tumor Models

Hydrogen peroxide (H2O2) overexpressed in mitochondria has been regarded as a key biomarker in the pathological processes of various diseases. However, there is currently a lack of suitable mitochondria-targetable near-infrared (NIR) probes for the visualization of H2O2 in multiple diseases, such as PM2.5 exposure-induced lung injury, hepatic ischemia-reperfusion injury (HIRI), nonalcoholic fatty liver (NAFL), hepatic fibrosis (HF), and malignant tumor tissues containing clinical cancer patient samples. Herein, we conceived a novel NIR fluorescent probe (HCy-H2O2) by introducing pentafluorobenzenesulfonyl as a H2O2 sensing unit into the NIR hemicyanine platform. HCy-H2O2 exhibits good sensitivity and selectivity toward H2O2, accompanied by a remarkable "turn-on" fluorescence signal at 720 nm. Meanwhile, HCy-H2O2 has stable mitochondria-targetable ability and permits monitoring of the up-generated H2O2 level during mitophagy. Furthermore, using HCy-H2O2, we have successfully observed an overproduced mitochondrial H2O2 in ambient PM2.5 exposure-induced lung injury, HIRI, NAFL, and HF models through NIR fluorescence imaging. Significantly, the visualization of H2O2 has been achieved in both tumor-bear mice as well as surgical specimens of cancer patients, making HCy-H2O2 a promising tool for cancer diagnosis and imaging-guided surgery.

A novel fluorescence probe for ultrafast detection of SO2 derivatives/biogenic amines and its multi-application: Detecting food and fish freshness, fluorescent dye and bioimaging

In this study, we have effectively prepared a novel fluorescent probe named HDXM based on benzopyran derivatives for the ultrafast detection (within 3 s) of SO2 derivatives or biogenic amines. HDXM showed a noticeable color change after the addition of SO2 derivatives (from purple to colorless) or biogenic amines (from purple to blue), indicating that HDXM can identify two analytes with the naked eye. It is worth noting that HDXM can be used to detect SO2 derivatives in actual sugar samples, and to image HSO3-/SO32- in living cells. More importantly, sensing labels (HDXM-loaded filter paper or agarose hydrogel) enable real-time visual monitoring of salmon freshness through colorimetric and fluorescence dual channels. Compared with the Chinese national standard method, the sensing label is an effective tool for evaluating the freshness of fish. Benefiting from its excellent solubility and fluorescence performance, HDXM can be used as a versatile fluorescent material in various applications, including flexible films, glass coatings, impregnating dyes, printing, and fingerprint ink. HDXM is expected to be a promising and valuable multifunctional tool for food safety and fluorescent materials.

A ratiometric fluorescence probe for bisulfite detection in live cells and meat samples

The development of reliable probe technology for the detection of bisulfite (HSO3-) in situ in food and biological samples is contributing significantly to food quality and safety assurance as well as community health. In this work, a responsive probe, EHDI, is developed for ratiometric fluorescence detection of HSO3- in aqueous solution, meat samples, and living cells. The probe is designed based on the HSO3- triggered 1,4-addition of electron deficit C = C bond of EHDI. As a result of this specific 1,4-addition, the π-conjugation system was destructed, resulting in blue shifts of the emission from 687 to 440 nm and absorption from 577 to 355 nm. The probe has good water solubility, high sensitivity and selectivity, allowing it to be used for imaging of HSO3- internalization and production endogenously. The capability of probe EHDI for HSO3- was then validated by traditional HPLC technology, enabling accurately detect HSO3- in beef samples. The successful development of this probe thus offers a new tool for investigating HSO3- in situ in food and biological conditions.

Near-Infrared Fluorescence Probe for Indication of the Pathological Stages of Wound Healing Process and Its Clinical Application

Chronic wound healing is one of the most complicated biological processes in human life, which is also a serious challenge for human health. During the healing process, multiple biological pathways are activated, and various kinds of reactive oxygen species participate in this process. Hydrogen peroxide (H2O2) involves in chronic wounds and its concentration is fluctuated in different pathological stages during the wound healing process. Therefore, H2O2 may be recognized as a powerful biomarker to indicate the wound healing process. However, the pathological roles of H2O2 cannot be fully understood yet. Herein, we proposed a near-infrared fluorescent probe DCM-H2O2 for highly sensitive and rapid detection of H2O2 in living cells and scald and incision wound mice models. DCM-H2O2 exhibited a low detection limit and high specificity with low cytotoxicity for H2O2, which had great potential for its application in vivo. The probe was successfully utilized to monitor the fluctuation of endogenous H2O2 in the proliferation process of human immortalized epidermal (HACAT) cells, which confirmed that H2O2 participated in the cells' proliferation activity through a growth factor signaling pathway. In the scald and incision wound mice models, H2O2 concentration fluctuations at different pathological stages during the wound healing process could be obtained by in vivo fluorescence imaging. Finally, H2O2 concentrations in different stages of human diabetic foot tissues were also confirmed by the proposed probe. We expect that H2O2 could be a sensitive biomarker to indicate the wound healing process.

Pentafluorobenzene: Promising Applications in Diagnostics and Therapeutics

Pentafluorobenzene (PFB) represents a class of aromatic fluorine compounds employed exclusively across a spectrum of chemical and biological applications. PFBs are credited with developing various chemical synthesis techniques, networks and biopolymers, bioactive materials, and targeted drug delivery systems. The first part of this review delves into recent developments in PFB-derived molecules for diagnostic purposes. In the latter segment, PFB's role in the domain of theragnostic applications is discussed. The review elucidates different mechanisms and interaction strategies applied in leveraging PFBs to formulate diagnostic and theragnostic tools, substantiated by proper examples. The utilization of PFBs emerges as an enabler, facilitating manifold reactions, improving materials' properties, and even opening avenues for explorative research.

A new lysosome-targeted fluorescent probe for hydrogen peroxide based on a benzothiazole derivative

As an important member of reactive oxygen species, hydrogen peroxide (H2O2) plays a key role in oxidative stress and cell signaling. Abnormal levels of H2O2 in lysosomes can induce damage or even loss of lysosomal function, leading to certain diseases. Therefore, real-time monitoring of H2O2 in lysosomes is very important. In this work, we designed and synthesized a novel lysosome-targeted fluorescent probe for H2O2-specific detection based on a benzothiazole derivative. A morpholine group was used as a lysosome-targeted unit and a boric acid ester was chosen as the reaction site. In the absence of H2O2, the probe exhibited very weak fluorescence. In the presence of H2O2, the probe showed an increased fluorescence emission. The fluorescence intensity of the probe for H2O2 displayed a good linear relationship in the concentration range of H2O2 from 8.0 × 10-7 to 2.0 × 10-4 mol·L-1. The detection limit was estimated to be 4.6 × 10-7 mol·L-1 for H2O2. The probe possessed high selectivity, good sensitivity and short response time for the detection of H2O2. Moreover, the probe had almost no cytotoxicity and had been successfully applied to confocal imaging of H2O2 in lysosomes of A549 cells. These results illustrated that the developed fluorescent probe in this study could provide a good tool for the determination of H2O2 in lysosomes.

Evaluation of peroxynitrite fluxes in inflammatory mice with a ratiometric fluorescence probe

Inflammation is a critical physiological process in the human body, which is closely related to numerous disorders and cancers. ONOO^- is generated and functionalized in the inflamed process, but the roles of ONOO^- are still blurred. To illuminate the roles of ONOO^-, we fabricated an intramolecular charge transfer (ICT)-based fluorescence probe, HDM-Cl-PN, for the ratiometric determination of ONOO^- in the inflamed mouse model. The probe displayed a gradual fluorescence increase at 676 nm and a fluorescence drop at 590 nm toward 0-10.5 μM ONOO^-, and the ratio of 676 nm fluorescence and 590 nm fluorescence varied from 0.7 to 24.7. The significantly changed ratio and favorable selectivity ensure the sensitive detection of subtle changes in cellular ONOO^-. Thanks to the excellent sensing performance, HDM-Cl-PNin vivo ratiometrically visualized ONOO^- fluctuations in the LPS-triggered inflammatory process. Overall, this work not only expatiated the rational design for a ratiometric ONOO^- probe but also built a bridge to investigate the connections between ONOO^- and inflammation in living mice.

Recent progress in the development of fluorescent probes for imaging pathological oxidative stress

Oxidative stress is closely related to the physiopathology of numerous diseases. Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) are direct participants and important biomarkers of oxidative stress. A comprehensive understanding of their changes can help us evaluate disease pathogenesis and progression and facilitate early diagnosis and drug development. In recent years, fluorescent probes have been developed for real-time monitoring of ROS, RNS and RSS levels in vitro and in vivo. In this review, conventional design strategies of fluorescent probes for ROS, RNS, and RSS detection are discussed from three aspects: fluorophores, linkers, and recognition groups. We introduce representative fluorescent probes for ROS, RNS, and RSS detection in cells, physiological/pathological processes (e.g., Inflammation, Drug Induced Organ Injury and Ischemia/Reperfusion Injury etc.), and specific diseases (e.g., neurodegenerative diseases, epilepsy, depression, diabetes and cancer, etc.). We then highlight the achievements, current challenges, and prospects for fluorescent probes in the pathophysiology of oxidative stress-related diseases.

Evaluating the Accuracy of FUCCI Cell Cycle In Vivo Fluorescent Imaging to Assess Tumor Proliferation in Preclinical Oncology Models

PURPOSE

The primary goal of this study is to evaluate the accuracy of the fluorescence ubiquitination cell cycle indicator (FUCCI) system with fluorescence in vivo imaging compared to 3'-deoxy-3'-[18F]fluorothymidine ([18F]-FLT) positron emission tomography (PET)/computed tomography (CT) and biological validation through histology. Imaging with [18F]-FLT PET/CT can be used to noninvasively assess cancer cell proliferation and has been utilized in both preclinical and clinical studies. However, a cost-effective and straightforward method for in vivo, cell cycle targeted cancer drug screening is needed prior to moving towards translational imaging methods such as PET/CT.

PROCEDURES

In this study, fluorescent MDA-MB-231-FUCCI tumor growth was monitored weekly with caliper measurements and fluorescent imaging. Seven weeks post-injection, [18F]-FLT PET/CT was performed with a preclinical PET/CT, and tumors samples were harvested for histological analysis.

RESULTS

RFP fluorescent signal significantly correlated with tumor volume (r = 0.8153, p < 0.0001). Cell proliferation measured by GFP fluorescent imaging was correlated with tumor growth rate (r = 0.6497, p < 0.001). Also, GFP+ cells and [18F]-FLT regions of high uptake were both spatially located in the tumor borders, indicating that the FUCCI-IVIS method may provide an accurate assessment of tumor heterogeneity of cell proliferation. The quantification of total GFP signal was correlated with the sum of tumor [18F]-FLT standard uptake value (SUV) (r = 0.5361, p = 0.0724). Finally, histological analysis confirmed viable cells in the tumor and the correlation of GFP + and Ki67 + cells (r = 0.6368, p = 0.0477).

CONCLUSION

Fluorescent imaging of the cell cycle provides a noninvasive accurate depiction of tumor progression and response to therapy, which may benefit in vivo testing of novel cancer therapeutics that target the cell cycle.

Water-Dispersible Activatable Nanoprobe for Detecting Cadmium-Ion-Induced Oxidative Stress in Edible Crops via Near-Infrared Second-Window Fluorescence Imaging

Edible crops are important in terms of food security and sustainable agriculture. Heavy-metal-ion contamination of water/soil has deleterious impacts on the growth of edible crops. Among the heavy metals, cadmium (Cd) is toxic to plants, people, and animals, as it is widely used in industry; it has become the most important metal ion in the soil/water pollution. Once the toxic Cd ion enters edible crops via the water/soil in which the crops grow, it will induce oxidative stress (overproduction of reactive oxygen species with H₂O₂ being the most abundant) in the crops, and strong oxidative stress leads to the crops' growth depression or inhibition. Hence, it is of great significance to accurately monitor the oxidative stress induced by Cd ions in edible crops, as the monitoring results could be employed for the early warning of Cd-ion pollution in water/soil. Herein, we design an activatable nanoprobe that can detect Cd-ion-induced oxidative stress in edible crops via near-infrared second-window (NIR-II) fluorescence imaging. The molecular probe IXD-B contains the diphenylamine-modified xanthene group acting as the electron-donating unit, bis(methylenemalononitrile)indan as the electron-accepting unit, and the methenephenylboronic acid group as the recognition moiety for H₂O₂ and the fluorescence quencher. The probe molecules being encapsulated by the amphiphilic DSPE-PEG2000 render the water-dispersible nanoprobe (IXD-B@DSPE-PEG2000). When the nanoprobe enters the edible crops, it can be activated by the overexpressed H₂O₂ therein and consequently emit strong NIR-II fluorescence signals for visualizing and tracking the oxidative stress in edible crops induced by Cd ions.

H2O2-Activated NIR-II Fluorescent Probe with a Large Stokes Shift for High-Contrast Imaging in Drug-Induced Liver Injury Mice

Drug-induced liver injury (DILI) is the most common clinical adverse drug reaction, which is closely associated with the oxidative stress caused by overproduced reactive oxygen species. Hepatic H₂O₂, as an important biomarker of DILI, plays a crucial role in the progression of DILI. However, there remains a challenge to develop H₂O₂-activatable second near-infrared (NIR-II, 1000-1700 nm) small molecular probes with both a large Stokes shift and a long emission wavelength beyond 950 nm. Herein, we developed an activatable NIR-II fluorescent probe (IR-990) with an acceptor-π-acceptor (A-π-A) skeleton for real-time detection of H₂O₂ in vivo. In the presence of H₂O₂, nonfluorescent probe IR-990 was successfully unlocked by generating a donor-π-acceptor (D-π-A) structure and switched on intense NIR-II fluorescence, exhibiting a peak emission wavelength at 990 nm and a large Stokes shift of 200 nm. Moreover, it was able to detect H₂O₂ with high sensitivity and selectivity in vitro (LOD = 0.59 μM) and monitor the behavior of endogenous H₂O₂ in the HepG2 cell model of DILI for the first time. Notably, probe IR-990 was successfully applied in real-time imaging of endogenous H₂O₂ generation in the DILI mouse model, showing a high signal-to-background ratio of 11.3/1. We envision that IR-990 holds great potential as a powerful diagnosis tool for real-time visualization of H₂O₂ in vivo and revealing the mechanism of DILI in the future.

Acetyl group assisted rapid intramolecular recognition of hydrogen peroxide: A novel promising approach for efficient hydrogen peroxide probe

As a vital biomolecule, hydrogen peroxide (H₂O₂) is involved in many physiological and pathological processes. Therefore, it is important to detect H₂O₂ in vivo conveniently and efficiently. In this paper, we report a new method of nucleophilic addition of H₂O₂ to the acetyl group to promote the rapid intramolecular reaction, which can be used to develop an efficient H₂O₂ probe. Based on this unique auxiliary recognition part, a fluorescent probe for H₂O₂ detection was designed and synthesized. This probe has the advantages of high sensitivity (limits of detection 7.0 × 10^-8 M or even lower.), fast response (within 3 min) and large Stokes shift (225 nm), which not only can monitor exogenous and endogenous H₂O₂ in cells but also successfully achieves the change of endogenous H₂O₂ level caused by drug sexual organ injury in zebrafish.

Recent advances in dual-target-activated fluorescent probes for biosensing and bioimaging

Fluorescent probes have been powerful tools for visualizing and quantifying multiple dynamic processes in living cells. However, the currently developed probes are often constructed by conjugation a fluorophore with a recognition moiety and given signal-output after triggering with one singly target interest. Compared with the single-target-activated fluorescent probes mentioned above, the dual-target-activated ones, triggering with one target under stimulus (such as photoirradiation, microenvironment) or another targets, have the advantages of advoiding nonspecific activation and "false positive" results in complicated environments. In recent years, many dual-target-activated fluorescent probes have been developed to detect various biologically relevant species. In view of the importance of a comprehensive understanding of dual-target- activated fluorescent probes, a thorough summary of this topic is urgently needed. However, no comprehensive and critical review on dual target activated fluorescent probes has been published recently. In this review, we focus on the dual-target-activated fluorescent probes and briefly outline their types and current state of development. In each type, the chemical structure, proposed responsive mechanism and application of probes are highlighted. At last, the challenges and prospective opportunities of every type were proposed.

Recent Progress in Organic Small-Molecule Fluorescent Probe Detection of Hydrogen Peroxide

The fluorescent probe has become an important method for accurate detection of H2O2, with advantages of simple operation, high sensitivity, good selectivity, and real-time dynamic monitoring. This paper reviews the research progress in organic small-molecule fluorescent probe H2O2 detection methods that are based on different recognition reactions. In addition, the application prospect of fluorescent probes in the detection of trace H2O2 is anticipated.

Target-Binding Accelerated Response for Sensitive Detection of Basal H2O2 in Tumor Cells and Tissues via a Dual-Functional Fluorescence Probe

Aberrant production of H₂O₂ is involved in cancer. The levels of H₂O₂ are significantly higher in tumor cells than in normal cells. It is important to develop fluorescent probes to image basal H₂O₂ selectively in tumor cells. So far, a cancer cell-targeting probe to image basal H₂O₂ has not been reported. Thus, we developed a fluorescent probe, BBHP, which contains benzil as a H₂O₂-recognition site and biotin as a target binding motif for the selective and sufficient detection of H₂O₂ in tumor cells. BBHP enables a selective fluorescence turn-on response to H₂O₂. The binding of the probe with biotin receptors can greatly accelerate the fluorescence response to H₂O₂. As a result, BBHP can sufficiently image basal H₂O₂ in biotin receptor-positive cancer cells and tumor tissues. Finally, BBHP was successfully applied to discriminate between cancerous and normal tissues.

A ROS-responsive, self-immolative and self-reporting hydrogen sulfide donor with multiple biological activities for the treatment of myocardial infarction

Myocardial infarction (MI), as one of the leading causes of global death, urgently needs effective therapies. Recently, hydrogen sulfide (H₂S) has been regarded as a promising therapeutic agent for MI, while its spatiotemporally controlled delivery remains a major issue limiting clinical translation. To address this limitation, we designed and synthesized a novel H₂S donor (HSD-R) that can produce H₂S and emit fluorescence in response to reactive oxygen species (ROS) highly expressed at diseased sites. HSD-R can specifically target mitochondria and provide red fluorescence to visualize and quantify H₂S release in vitro and in vivo. Therapeutically, HSD-R significantly promoted the reconstruction of cardiac structure and function in a rat MI model. Mechanistically, myocardial protection is achieved by reducing cardiomyocyte apoptosis, attenuating local inflammation, and promoting angiogenesis. Furthermore, inhibition of typical pro-apoptotic genes (Bid, Apaf-1, and p53) played an important role in the anti-apoptotic effect of HSD-R to achieve cardioprotection, which were identified as new therapeutic targets of H₂S against myocardial ischemia injury. This ROS-responsive, self-immolative, and fluorescent H₂S donor can serve as a new theranostic agent for MI and other ischemic diseases.

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A reactive oxygen species-responsive and self-reporting H₂S donor (HSD-R) is developed for controlled H₂S delivery.

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HSD-R shows desirable fluorescence for imaging H₂S release upon triggering by reactive oxygen species.

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HSD-R displays significant cardioprotective effects in rats.

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HSD-R exhibits multiple biological activities including anti-apoptotic, anti-inflammatory, and pro-angiogenic effects.

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Anti-apoptotic activity of HSD-R is due to inhibiting the expression of several pro-apoptotic factors.

Two-photon fluorescence and MR bio-imaging of endogenous H2O2 in the tumor microenvironment using a dual-mode nanoprobe

The dual-mode bio-imaging nanoprobe TP-CQDs@MnO2, based on two-photon carbon quantum dots and MnO2, has been developed for the two-photon fluorescence and MR imaging of endogenous H2O2 in the tumor microenvironment, and it achieved high selectivity, a great signal-to-noise ratio, a limit of detection (LOD) of 1.425 pM for H2O2, and a two-photon tissue penetration depth of 280 μm.

Real-Time Evaluation of Hydrogen Peroxide Injuries in Pulmonary Fibrosis Mice Models with a Mitochondria-Targeted Near-Infrared Fluorescent Probe

Pulmonary fibrosis is a fatal chronic lung disease, leading to poor prognosis and high mortality. Accumulating evidence suggests that oxidative stress characterized by excessive production of hydrogen peroxide (H₂O₂) is an important molecular mechanism causing pulmonary fibrosis. We conceive a new type of mitochondria-targeted near-infrared fluorescent probe Mito-Bor to investigate changes in the level of endogenous H₂O₂ in living cells and mice models with pulmonary fibrosis. In the design strategy of the Mito-Bor probe, we selected azo-BODIPY as the fluorophore owing to its near-infrared fluorescence, strong photochemical stability, and low biological toxicity. Under physiological conditions, the response moiety 4-bromomethylphenylboronic acid pinacol ester could easily detect H₂O₂, and turn the fluorescence switch on. The modification of the lipophilic triphenylphosphine cation on the fluorophore would allow the probe to easily pass through the phospholipid bilayer of cells, and the internal positive charge could contribute to the selectivity of the mitochondria accumulation. The Mito-Bor probe provides high selectivity, low limit of detection, high biocompatibility, and excellent photostability. It can be used to detect changes in the level of H₂O₂ in living cells and in vivo. Therefore, the probe is applied to investigate the fluctuation of the H₂O₂ level during the process of inducing pulmonary fibrosis in cells, with changes in its fluorescence intensity correlating with the concentration of H₂O₂ and indicating the level of oxidative stress in fibroblasts. Conversely, pulmonary fibrosis can be modulated by adjusting the level of H₂O₂ in cells. A further study in mice models of bleomycin-induced pulmonary fibrosis confirms that NADPH oxidase 4 (NOX4) acts as a "button" to regulate H₂O₂ levels. The direct inhibition of NOX4 can significantly reduce the level of H₂O₂, which can delay the progression of lung fibrosis. These results provide an innovative way for the clinical treatment of pulmonary fibrosis.

Regulation of Mitochondrial Dynamics in Parkinson's Disease-Is 2-Methoxyestradiol a Missing Piece?

Mitochondria, as "power house of the cell", are crucial players in cell pathophysiology. Beyond adenosine triphosphate (ATP) production, they take part in a generation of reactive oxygen species (ROS), regulation of cell signaling and cell death. Dysregulation of mitochondrial dynamics may lead to cancers and neurodegeneration; however, the fusion/fission cycle allows mitochondria to adapt to metabolic needs of the cell. There are multiple data suggesting that disturbed mitochondrial homeostasis can lead to Parkinson's disease (PD) development. 2-methoxyestradiol (2-ME), metabolite of 17β-estradiol (E2) and potential anticancer agent, was demonstrated to inhibit cell growth of hippocampal HT22 cells by means of nitric oxide synthase (NOS) production and oxidative stress at both pharmacologically and also physiologically relevant concentrations. Moreover, 2-ME was suggested to inhibit mitochondrial biogenesis and to be a dynamic regulator. This review is a comprehensive discussion, from both scientific and clinical point of view, about the influence of 2-ME on mitochondria and its plausible role as a modulator of neuron survival.

A lysosome-targeted fluorescent probe for the specific detection and imaging of formaldehyde in living cells

We presented herien the rational design, synthesis, and photophysical property studies of the lysosome-targeted fluorescence FA probe NP-Lyso, an isopropyl group modified ortho-diaminonaphthalimide derivative. After the reaction of FA and ortho-phenylenediamine modified with the isopropyl group in NP-Lyso, the probe exhibited favorable features such as a large fluorescence enhancement, specific selectivity and high sensitivity for the detection of FA. More importantly, NP-Lyso could be used to detect and image endogenous FA in lysosomes. In light of these prominent properties, we envision that NP-Lyso will be an efficient optical imaging approach for investigating the biofunctions of FA in living systems.

Photoexcited molecular probes for selective and revertible imaging of cellular reactive oxygen species

Redox homeostasis is key to maintaining the normal physiological status of living cells.

A bifunctional mitochondrial targeting AIE-active fluorescent probe with high sensitivity to hydrogen peroxide and viscosity for fatty liver diagnosis

A mitochondrial targeting AIE-active fluorescent probe with highly sensitive dual-detection of hydrogen peroxide and viscosity for fatty liver diagnosis.

Ultra-fast synthesis of water soluble MoO3-x quantum dots with controlled oxygen vacancies and their near infrared fluorescence sensing to detect H2O2

We report a facile method for the synthesis of water soluble MoO_3-x quantum dots (QDs) at room temperature by injecting hydrochloric acid and mercaptosuccinic acid into ammonium molybdate solution within 5 seconds. The optical properties and oxygen vacancy concentration of the QDs could be well controlled by the competitive absorption of a carboxyl group and sulfhydryl group of the ligand with QDs by coordination interaction. The obtained QDs could be used as near infrared region (NIR) fluorescence probes to detect hydrogen peroxide with a low detection limit (3 nM).

A Highly Selective and Sensitive Chemiluminescent Probe for Real-Time Monitoring of Hydrogen Peroxide in Cells and Animals

Selective and sensitive molecular probes for hydrogen peroxide (H₂ O₂ ), which plays diverse roles in oxidative stress and redox signaling, are urgently needed to investigate the physiological and pathological effects of H₂ O₂ . A lack of reliable tools for in vivo imaging has hampered the development of H₂ O₂ mediated therapeutics. By combining a specific tandem Payne/Dakin reaction with a chemiluminescent scaffold, H₂ O₂ -CL-510 was developed as a highly selective and sensitive probe for detection of H₂ O₂ both in vitro and in vivo. A rapid 430-fold enhancement of chemiluminescence was triggered directly by H₂ O₂ without any laser excitation. Arsenic trioxide induced oxidative damage in leukemia was successfully detected. In particular, cerebral ischemia-reperfusion injury-induced H₂ O₂ fluxes were visualized in rat brains using H₂ O₂ -CL-510, providing a new chemical tool for real-time monitoring of H₂ O₂ dynamics in living animals.

Highly Efficient Cell Membrane Tracker Based on a Solvatochromic Dye with Near-Infrared Emission

The cell membrane is composed of a phospholipid bilayer with embedded proteins and maintains cell homeostasis through dynamic changes. An abnormal cell membrane shape could be a sign of unhealthy cells. Probes for subcellular fluorescence imaging that can identify the abnormal plasma membrane and record the dynamic changes are needed. Based on a solvatochromic dye with a near-infrared emission strategy, the amphipathic molecule (E)-2,2'-((4-(2-(4-(dicyanomethylene)-4H-chromen-2-yl)vinyl)phenyl)azanediyl)bis(ethane-1-sulfonic acid) (MRL) contained a hydrophilic sulfo group and a hydrophobic chromone group, which was designed and synthesized for staining the cell membrane and monitoring the morphology of the membranes under different conditions. MRL exhibited an excellent photostability and low cytotoxicity; when cells were incubated with MRL, cell membranes were specifically labeled. MRL is capable of long-term monitoring of the morphological changes of cell membrane.

A novel self-calibrating strategy for real time monitoring of formaldehyde both in solution and solid phase

Formaldehyde (FA) is a chemical substance with tremendously noxious feature for human health and it causes serious damages to living organisms. The recognition of formaldehyde in the form of fluorescent signals has been extensively explored by using a few molecular scaffolds in buffer mediums. In particular, the study for sensing of formaldehyde both in solution and solid state has generated considerable interests. Herein, a new ratiometric fluorescent probe 1-(5-(9-phenyl-9H-carbazol-3-yl)thiophen-2-yl)but-3-en-1-amine (SO-GJP) has been synthesized for selective detection of FA based on aza-Cope reaction. In the presence of FA from 0 to 1.3 mM, the emission band of SO-GJP varies from 393 nm to 542 nm and the detection limit has been calculated to be 1.55 μM. The entrapment of SO-GJP onto the thin layer chromatography (TLC) plate leads to the successful detection of FA with sensitive color change from white to yellow. Moreover, the response mechanism has been explained by FA-induced 2-aza-Cope rearrangement within SO-GJP and the chemical processes are supported by density functional theory, fluorescence and UV-vis spectra. The integration of responsive units based on carbazole platform can serve as one of the powerful strategies by directly converting signals at different circumstances into fluorescence.

In vivo real-time tracking of tumor-specific biocatalysis in cascade nanotheranostics enables synergistic cancer treatment

Glucose oxidase (GOD)-based synergistic cancer therapy has aroused great research interest in the context of cancer treatment due to the inherent biocompatibility and biodegradability. However, this emerging therapeutic system still lacks a strategy to predict and regulate the in vivo biocatalytic behavior of GOD in real time to minimize the side effects on normal tissues. Herein, we developed a tumor-specific cascade nanotheranostic system (BNG) that combines GOD-catalyzed oxidative stress and dual-channel fluorescent sensing, significantly improving the synergistic therapeutic efficacy with real-time feedback information. The nanotheranostic system remains completely silent in the blood circulatory system and selectively releases GOD enzymes in the tumor site, with enhanced near-infrared (NIR) fluorescence at 825 nm. Subsequently, GOD catalyzes H2O2 production, triggering cascade reactions with NIR fluorescence at 650 nm as an optical output, along with GSH depletion, enabling synergistic cancer treatment. The designed nanotheranostic system, integrated with tumor-activated cascade reactions and triggering a dual-channel output at each step, represents an insightful paradigm for precise cooperative cancer therapy.

Bioimaging of Glutathione with a Two-Photon Fluorescent Probe and Its Potential Application for Surgery Guide in Laryngeal Cancer

As the most abundant nonprotein biothiol in living cells, glutathione (GSH) prevents cellular components from oxidative damage and maintains the intracellular redox homeostasis. For further exploring whether GSH can be employed as a bioindicator to discriminate tumor lesion at a cellular level, the highly selective detection and accurate quantification of GSH under pathological conditions are critical. Herein, we design a coumarin derivative-based two-photon fluorescent probe Cou-Br for the detection of GSH in living cells, mice models, and clinical specimens. The prepared probe is capable of sensitively and selectively detecting GSH in complex biological systems. Cou-Br displays a good linear relationship in response to GSH and a low limit of detection. With the fluorescence signal positively associated with intracellular GSH levels, the probe enables real-time imaging of GSH in various cell lines. Under the condition of CS₂ stimulation, Cou-Br can rapidly respond to the fluctuation of intracellular GSH induced by oxidative damage. Furthermore, the in situ and in vivo bioimaging performances of Cou-Br are demonstrated. Typically, relying on the different cellular concentrations of GSH, the probe is successfully employed to identify the human laryngeal cancer lesion with outstanding capabilities of deep tissue imaging and tumor margin recognition. We assume that the abnormal expression level of GSH may be utilized as a potential bioindicator to discriminate tumor tissues from the surrounding disease-free tissues. To conclude, the proposed probe Cou-Br may potentially serve as a powerful chemical tool for the surgical navigation of cancer in clinic.

A novel fluorescent probe for rapidly detection cysteine in cystinuria urine, living cancer/normal cells and BALB/c nude mice

Cysteine (Cys), an important organic small molecule containing sulfhydryl groups, plays paramount functions in human pathologies and physiologies. The detection of Cys in living vivo is essential for studying its roles. Here, we designed and synthesized a novel red-emission fluorescent probe AXPI-Cys with highly sensitivity (LOD = 48.9 ± 0.23 nM), rapidly response (<7 min) and colorimetric for detection cysteine. More importantly, the AXPI-Cys was determined Cys in real cystinuria urine samples for the first time with the satisfactory results (92%-99.96%) and employed for specifically location of endogenous/exogenous Cys in living cancer/normal cells and almost non-toxic, that is very valuable for diagnosis of cystinuria and observation of the distribution of Cys in normal cells. Notably, the AXPI-Cys was applied to imaging Cys in BALB/c nude mice with good biocompatibility and desirable tissue-penetration depth. Owing to the superior capability of AXPI-Cys, it provided a desired method to detect Cys in urine samples and cells, and exhibited munificent potential usage in biosystems and imaging studies in vivo.

A new "off-on" NIR fluorescence probe for determination and bio-imaging of mitochondrial hypochlorite in living cells and zebrafish

Hypochlorite anion (ClO^-) has been recognized as host defense destructing incursive bacteria and pathogens, a signal molecule inducing occurrence of apoptosis and a noxious agent when it is overproduced. It is significant to detect ClO^- in mitochondria for getting meaningful physiological and pathological information. Compared with the fluorescence probes of emission wavelength in ultraviolet or visible region, those with near-infrared (NIR) fluorescence signal are advantageous due to the deeper tissue penetrability and less photo-bleaching effect. In this work, a new "off-on" NIR ClO^--specific fluorescence probe (Mito-NClO) especially located in mitochondria was designed and synthesized by condensation of diaminomaleonitrile with a new fluorophore (Mito-NCHO). A marked "turn-on" NIR fluorescence signal was observed on account of the oxidation of the imine bond by NaClO. Moreover, in the range from 0 to 20 μM, this probe had the capability to quantitatively detect ClO^- with a detection limit as low as 90.2 nM. Additionally, the probe exerted other excellent properties, including larger stokes shift (117 nm), better aqueous solubility, high selectivity toward ClO^-, rapid response and selective mitochondrial location. Furthermore, the bio-imaging experiments clearly demonstrated that Mito-NClO facilitated the visualization of exogenous and endogenous ClO^- in living HeLa cells and zebrafish model. Therefore, we speculate that the probe Mito-NClO can be served as an ideal tool for the monitoring of ClO^- in biosystems.

Research progress in the development of organic small molecule fluorescent probes for detecting H2O2

Hydrogen peroxide (H2O2), as an important signaling molecule during biological metabolism, is a key member of the reactive oxygen species (ROS) family. The excess of H2O2 will lead to oxidative stress, which is a crucial factor in the production of various ROS-related diseases. In order to study the diverse biological roles of H2O2 in cells and animal tissues, many methods have been developed to detect H2O2. Recently, fluorescence imaging has attracted more and more attention because of its high sensitivity, simple operation, experimental feasibility, and real-time online monitoring. Based on the response group, this study will review the research progress on hydrogen peroxide and summarizes the mechanisms, actualities and prospects of fluorescent probes for H2O2.

A new water-soluble two-photon fluorescent probe for detection of trace benzoyl peroxide in wheat flour and in living cell and tissue imaging

Benzoyl peroxide (BPO), a member of small-molecule reactive oxygen species (ROS), has attracted considerable attention because of its impact on human health and industrial importance.